A configuration of a receiver which receives a single carrier-frequency division multiple access (SC-FDMA) signal is shown in FIGS. 9 and 10. In addition, a mobile station performs transmission under the state in which one antenna is used and a rank is fixed to one.
FIG. 9 is a block diagram illustrating a configuration of a base station. Abase station 301 includes antennas 331-1 and 331-2; a duplexer 332; reception units 333-1 and 333-2; a cyclic prefix (CP) removal units 334-1 and 334-2; Fast Fourier Transform (FFT) units 335-1 and 335-2; demapping units 336-1 and 336-2; a sounding reference signal (SRS) channel estimation unit 337; a modulation and coding scheme (MCS) determination unit 338; a demodulation reference signal (DM-RS) channel estimation unit 339; a data channel demodulation/decoding unit 340; a control channel coding/modulation unit 341; an Inverse Fast Fourier Transform (IFFT) unit 342; a CP addition unit 343; and a transmission unit 344.
Each of the reception unit 333-1 and 333-2 converts a received signal having been received by a corresponding cue of the antennas 331-1 and 331-2 into a baseband signal. Each of the CP removal units 334-1 and 334-2 removes a CP from each of SC-FDMA symbols of the baseband signal. Each of the FFT units 335-1 and 335-2 performs, for each SC-FDMA symbol, FFT processing on the baseband signal resulting from the removal of the CPs and thereby transforms the baseband signal into a frequency-domain signal. Each of the den-tapping units 336-1 and 336-2 extracts an SRS, a DM-RS, and a data channel from the frequency-domain baseband signal.
The SRS channel estimation unit 337 calculates a first channel estimation value indicating a propagation-path state on the basis of the SRS. The MCS determination unit 338 calculates an MCS determination value, which is a transmission coding/modulation scheme for use in a next data-channel transmission by a mobile station, on the basis of the first channel estimation value supplied by the SRS channel estimation unit 337, and supplies the MCS determination value to the control channel coding/modulation unit 341. Here, an estimation value of a signal-to-interference pins noise power ratio (SINR) is calculated on the basis of the first channel estimation value, and the MCS determination value is determined on the basis of the calculated SINR estimation value by referring to a predetermined table in which each of MCS values is associated with a corresponding one of SINR ranges.
The DM-RS channel estimation unit 339 calculates a second channel estimation value indicating a propagation-path state on the basis of the DM-RS. The data channel demodulation/decoding unit 340 performs demodulation/decoding of the data channel by using the second channel estimation value.
The control channel coding/modulation unit 341 multiplexes the MCS determination value into a control channel, and performs coding and modulation of a resultant control channel. The IFFT unit 342 performs, for each of orthogonal frequency division multiplex (OFDM) symbols, IFFT processing on the modulated control channel and thereby transforms the modulated control channel into a time-domain baseband signal. The CP addition unit 343 adds, for each of the OFDM symbols, a CP to the time-domain baseband signal. The transmission unit 344 performs up-conversion of the baseband signal resulting from the addition of the CPs to convert the baseband signal into a radio frequency (RF) signal. The RF signal is transmitted, from the antenna 331-1 via the duplexer 332.
FIG. 10 is a block diagram illustrating a configuration of the DM-RS channel estimation unit 339. The DM-RS channel estimation unit 339 includes a multiplier unit 361; a complex conjugate unit 362; a frequency axis interpolation unit 363; an IFFT unit 364; a noise elimination unit 365; an FFT unit 366; a cat-off unit 367, and a time axis interpolation unit 368.
The complex conjugate unit 362 calculates a complex conjugate value of a known DM-RS sequence which is internally generated. The multiplier unit 361 multiplies a DM-RS, which results from demapping, by the complex conjugate value, and thereby removes modulated elements of the DM-RS. The frequency axis interpolation unit 363 performs interpolation processing in the frequency direction on a signal resulting from the removal of modulated elements included in the DM-RS by a difference number by which the number of actual sub-carriers is smaller as compared with the number of sampling points of art IFFT performed at a posterior stage (the difference number being associated with the number of unused sub-carriers). Here, as a method of the above interpolation processing, a method of interpolation processing shown in NPL 1 is employed.
Alternatively, as shown in PTL 2, a signal-noise ratio (SNR) is estimated, and in the case where the SNR is smaller than a predetermined threshold value, the interpolation processing is not performed and each of unused sub-carrier portions are fixedly made zero. The IFFT unit 364 performs IFFT processing on a signal resulting from the interpolation processing, and thereby generates a channel profile on the time axis. The noise elimination unit 365 eliminates noise elements of the channel profile on the time axis. The FFT unit 366 performs FFT processing on a signal resulting from the noise elimination, and thereby transforms the signal into a frequency domain signal. The cut-off unit 36 removes signals each having been interpolated through the interpolation processing on a corresponding one of the unused sob-carrier portions, from signals included in the frequency domain signal. The time axis interpolation unit 368 performs interpolation processing in the time direction on a frequency domain signal resulting from the removal of the signals having been interpolated on the unused sub-carrier portions, and calculates a channel estimation value for one sub-frame including portions in each of which any DM-RS is not multiplexed.
In PTL 1, there is disclosed a receiving device which estimates an impulse response by using a pilot signal which is disposed in a band whose width is narrower than that of a band on which an FFT is performed. This receiving device includes a reception unit that receives information data pieces and a pilot signal which are allocated for each of predetermined resources, and a propagation path estimation unit that calculates a propagation path estimation value by using the pilot signal, and a signal detection unit that detects the information data pieces. This propagation path estimation unit estimates the impulse response by using a pilot signal which has been transmitted by a transmitting device identical to a transmitting device having transmitted the information data pieces and which belongs to a resource different from a resource to which the information data pieces have been allocated.